The field of art to which this invention pertains is acid cleaning of rusty steel.
Rusty iron and steel surfaces have long been cleaned by sand blasting prior to being coated and painted. However, due to various air pollution laws, iron and steel fabricators have been resorting to acid cleaning to remove the rust. One method of acid cleaning is to spray the rusty surface with a hot aqueous solution of an acid, e.g., phosphoric acid, for a time sufficient to remove the rust. The acid drainoff is circulated through an ion exchange resin, make-up acid is added and the acid solution is reused. The acid treated steel surface must then be rinsed to remove residual acid and other contaminants left on the surface by the acid. If water is used as the rinse, the surface will begin to rust almost immediately. It is preferred to use a passivating rinse, i.e., a rinse which will render the steel passive to corrosion for a short period of time. Many of these rinses, however, interfere with the subsequent adhesion of protective coatings to the metal surface. Acid treatment (pickling), corrosion inhibition and passification of iron and steel are discussed in Kirk-Othmer "Encyclopedia of Chemical Technology", 2nd Ed., Vol. 6, pages 321-324, Vol. 13, pages 288-291.
U.S. Pat. No. 3,847,663 describes a method for cleaning the surfaces of metals during the processing of the metals, e.g., immediately after the metal is drawn. The foreign matter which is removed from the metal is chiefly drawing oils and the like. The cleaning compositions are aqueous solutions of alkali metal silicates and chloride plus, preferably, surfactants and chelating agents.
In U.S. Pat. No. 3,154,438, a method is described for preparing metal surfaces to receive an adherent coating of water soluble base paints by acid cleaning the metal followed by rinsing it with an aqueous amine solution.
In U.S. Pat. No. 3,368,913, acid treated steel is rinsed with an aqueous solution of a polyalkanolamine and an alkali.
Corrosion inhibitors containing a glycine, a chelating agent, phosphoric or boric acid ester and a water soluble divalent metal salt are described in U.S. Pat. No. 3,699,052.